As per document: https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/host-name-edit-system.html#host-name__d544856e43
You can also use the %s character to designate where to substitute the Routing Engine name. For example, on Routing Engine 1, set system host-name %s_my_host sets the hostname to re1_my-host.
%s
set system host-name %s_my_host
re1_my-host.
However, when host name is checked on show LLDP neighbor it do not show RE
Every time we configure %s and something else, the rest after %s is not showed on show lldp neighbor.
When configured:
re0-cr01.rdu101> show configuration | display set | match host
set groups re0 system host-name "%s-cr01.rdu101"
set groups re1 system host-name "%s-cr01.rdu101"
re0-cr01.rdu101>
This is a device that is directly connected to it, and you can see the name is not showing up correctly
dr01.rdu103 (wjennifer)# show lldp neighbor | match et-6
et-6/1/0 ae3 b4:f9:5d:ab:dd:67 et-0/0/6 re0.ultralab.juniper.net
et-6/3/0 ae3 b4:f9:5d:ab:dd:67 et-1/0/6 re0.ultralab.juniper.net
When configuring first the name of the router and then %s and it show it like this:
[email protected]# set groups re1 system host-name cr01.nuq237-%s-test
labroot@coriander-re0> show lldp neighbors
Local Interface Parent Interface Chassis Id Port info System Name
et-0/1/0 - 40:de:ad:98:6a:15 513 cr01.nuq237-re1.ultralab.juniper.net
et-0/1/1 - 40:de:ad:98:6a:15 514 cr01.nuq237-re1.ultralab.juniper.net
fxp0 - e8:24:a6:be:6d:cd 522 QNC-JTAC-LSW-E09-52
Clearly the behavior is not the expected. This was changed on higher EVO versions starting on 22.3R1-EVO
Now, you can use first the name and then %s or you can use the same configuration as on Junos, it works fine.
{master}[edit]
[email protected]# set groups re0 system host-name re0-cr01.rdu101
et-0/1/0 - 40:de:ad:98:6a:15 513 re0-cr01.rdu101.ultralab.juniper.net
et-0/1/1 - 40:de:ad:98:6a:15 514 re0-cr01.rdu101.ultralab.juniper.net